The present invention relates generally to catalogs in multiple data processing systems and more particularly to the sharing of catalogs in such a system.
In today""s information technology industry, customers desire systems that have better performance and cost improvements over their current systems, while permitting continued use of their existing applications. High availability is also important given today""s rising mobile workforce and ability for global connectivity through the Internet. Current processing system designs for information technology applications must provide scalable, granular growth, and continuous application availability. Clustering technology, such as IBM Corporation""s S/390 Parallel Sysplex, has been developed to achieve these design needs.
A cluster arrangement links individual data processing systems in a manner that creates a single, powerful system, which can support numerous users simultaneously. A cluster offers high availability and excellent scalability. If one system/node in the cluster fails, the other systems in the cluster continue to run.
In such a multiprocessor system, catalogs typically are used to categorize data. Typically, in cluster arrangements such as IBM""s S/390, an integrated catalog facility (ICF) structure is utilized to support shared catalogs. A catalog is a data set which contains information about other data sets. It provides users with the ability to locate a data set by name, without knowing where the data set resides. By cataloging data sets, users will need to know less about the storage setup. Thus, data can be moved from one device to another, without requiring a change in statements which refer to an existing data set.
Cataloging data sets simplifies backup and recovery procedures. Catalogs are the central information point for VSAM data sets: all VSAM data sets must be cataloged. In addition, all SMS-managed data sets must be cataloged.
In conventional systems, an ICF Catalog component supports shared catalogs by maintaining a local system cache of recently accessed catalog records in main memory on each system and a list of catalog updates in what is called a xe2x80x9csharing subcellxe2x80x9d in the data VSAM Volume Record (VVR) contained in the VSAM Volume Data Set (VVDS) on a DASD memory subsystem. Whenever a request is made to a shared catalog, the Catalog component must read the sharing subcell from the DASD memory subsystem, to verify the currency of the locally cached records on that system.
The local DASD subsystem is updated from the change information contained in the sharing subcell. If a catalog request involves a modification to the catalog, this information is written to the sharing subcell on the DASD subsystem. Significant overhead in terms of cross-system communication and long-duration I/O activity occurs for each such catalog request. Field experience indicates the elapsed time to process a request against a shared catalog can be up to five times longer than the same request against an unshared catalog.
In order for a system to access this data, the disk must be locked out from all other systems while the I/O operation executes. This approach is time-consuming and also makes the disk unavailable to other systems for relatively long periods of time. Accordingly, what is needed is a system and method which overcomes the above-mentioned problems. The present invention addresses such a need.
A method and system for sharing a catalog in a multiprocessor system is disclosed. The multiprocessor system includes a plurality of host systems. The method and system comprises storing an entire volume data record for the catalog in a shared processor. Thereafter, the method and system comprises reading sharing information of the catalog from the processor to the appropriate host system when the appropriate host system needs access to the catalog.
For example, in a S/390 parallel processor system an enhanced catalog sharing system (ECS) is utilized in conjunction with the catalogs. In this type of system, the entire data VSAM volume record (VVR) for an ECS-active catalog is stored in a coupling facility processor. This processor is accessed using components of the S/390 product. When an ECS-active host system needs access to an ECS-active catalog, the sharing information is read in from the coupling facility processor instead of a DASD volume. If the shared catalog request involves an update to the ECS-active catalog, the (VVR) in the coupling facility is updated; no writes are performed to DASD for updates to the sharing subcell.
By storing the sharing control data on a shared processor, the I/O operations and the disk lock outs are eliminated, dramatically decreasing elapsed time for a shared catalog request and increasing the availability of the disk device. This results in a significant performance improvement, with shared catalog performance approaching that of unshared catalogs.